Pneumatic void detector



Dec. 24, 1963 GQFQRRESTER PNEUMATIC VOID DETECTOR 2 Sheets-Sheet 1 FiledDec. 9, 1960 INVENTOR.

ATTORN EYS Dec. 24, 1963- e. FORRESTER 3,115,037

PNEUMATIC VOID DETECTOR Filed Dec- 9, 1960 2 Sheets-Sheet 2 INDICATORFIGG 22 62 Fl 46 I8 I 42 34 I V I0 79 2O 32 INDICATOR INVENTOR 68 Z I Z5 INDICATOR BY 7 Q ewl wfiw ATTORNEYS United States Patent 3,115,037PNEUMATIC VOID DETECTOR Gilbert Forrester, Falmouth, Maine, assignor toS. D. Warren Company, Boston, Mass., a corporation of MassachusettsFiled Dec. 9, 1960, Ser. No. 74,873 3 Claims. (Cl. 73159) This inventionrelates to apparatus for use in the control of quality of a moving webof flexible material, and more particularly to apparatus for detectingvoids in a moving web of paper.

In the manufacture of paper it is necessary at some stage in the processto inspect the paper for voids, or holes, which may exist and whichrender the paper unsatisfactory in quality.

It is possible to examine each sheet of finished paper by eye, howeversuch procedure is too slow and too costly to be economically feasible.It is also too fallible. Consequently, devices have been provided underthe teachings of the prior art to accomplish such void detection bymechanical means. These devices have not proven wholly satisfactory. Forexample, a device may be constructed wherein a wheel or other contactelement is positioned on the web of paper as it passes over a roller.When a void passes under the wheel, the wheel contacts the rollerclosing an electrical circuit which actuates a suitable indicator. Atleast two difficulties are inherent in this system. Firstly, the voidmay be simply in the nature of a razor-slit and hence not large enoughto be detected by the wheel. Secondly, a great number of such contactmaking devices are required to cover the entire width of a moving web ofpaper.

A second method of detecting voids in a moving web of flexible materialsuch as paper, is to position a source of light on one side of the weband means for detecting changes in the intensity of the light on theopposite side of the web. Again, such devices are unable to detect voidssuch as a razor-slit or a void having a flap of torn material covering ahole.

Accordingly, it is an object of my invention to provide apparatus whichwill detect any void in a moving web of paper, including a razor-slitand a void being covered by a flap.

It is another object of my invention to provide void detecting apparatusfor use with a moving web of paper which is effective over substantiallythe whole Width of the moving web.

In the accomplishment of these objects in a preferred embodiment of myinvention I construct a void detector having a rectangular base on whichis mounted an engagement head. The apparatus is positioned with the webof paper passing over the engagement head which is provided with aslightly curved top face. A longitudinal opening is formed along the topof the engagement head and is divided by walls into a series of shorteropenings or slots. Each shorter slot communicates with an independentinternal chamber formed by cooperating openings cut in the base and inthe engagement head. A diaphragm of flexible material is sandwichedbetween the base and the engagement head and divides each of thechambers into an upper and lower chamber. A spring loaded electricalcontact member is positioned extending up through the base and into thelower chamber and terminating in electrically conductive washers on thediaphragm. A passage communicating the upper chamber with a vacuum lineis provided whereby a vacuum may be drawn through the upper chamber andthe associated short slot in the top of the engagement head. The paperis then drawn across the series of slots and when a void passes over aslot, air is admitted to the associated chamber and thereby releases thevacuum therein causing the spring loaded contact member and associateddiaphragm to descend. A second contact member is positioned below thediaphragm and contact washers and the descent of the diaphragm causes anengagement of the two contact members thereby actuating appropriateregistering devices. In order to detect creases in the web as well asvoids, longitudinal openings positioned in a spaced relationship to thelongitudinal slots are provided through which air at atmosphericpressure may communicate with the web just prior to its passing over thelongitudinal slots whereby the air may flow through a crease into thelongitudinal slots. Similar openings just subsequent to the slotsfacilitate the disengagement of the paper from the apparatus.

It is a feature of my invention to provide detector chambers in whichchanges in air pressure are employed to detect voids in a moving web.

It is a further feature of my invention to provide a detector forcreases, wrinkles and similar surface irregularities as well as voids.

It is another feature of my invention to provide a series oflongitudinal substantially contiguous detector areas disposedtransversely to the moving web whereby a void signal may be registeredgenerally if a void passes any detector area or may be registered insuch fashion as to indicate the specific detector area which detectedthe void.

These and other objects and features of my invention will appear as thedescription proceeds with the aid of the accompanying drawings in which:

FIG. 1 is a view in perspective of my invention partially cut away toshow the disposition of the interior elements;

FIG. 2 is an exploded view of the base, diaphragm and engagement head;

FIG. 3 is a fragmentary view in perspective showing the apparatus inposition for operation;

FIG. 4 is a sectional view along the line 4-4 of FIG. 1 showing thepositions of the internal elements during operation of the apparatuswhen no void is present;

FIG. 5 is a view similar to FIG. 4 showing the position of the interiorelements when a void is detected;

FIG. 6 is a view in section similar to FIG. 4 showing the position ofthe interior elements in an alternative embodiment of my invention; and

FIG. 7 is a view similar to FIG. 6 showing the position of the interiorelements when a void is detected.

Having reference to the above mentioned drawings for a more particulardescription of my invention in a preferred embodiment thereof, Iconstruct a base It) preferably of Lucite or a similar plastic providedwith a series of downwardly extending circular openings indicatedgenerally at 12 which are formed so as not to extend through the bottomof the base 10. An engagement head 14 of brass or other suitablematerial is provided having circular openings 16 which extend upwardlyfrom the bottom of the head 14. A circular opening 16 is provided foreach circular opening 12 in the base 10, and is positioned to be coaxialand of equal radius therewith when the apparatus is assembled.

Sandwiched between the base 10 and head 14 is a sheet of flexiblematerial forming a diaphragm 18. In the preferred embodiment arubberized fabric is employed. The base 10, diaphragm 18, and head 14are secured together in an airtight relationship by a plurality ofmachine screws 20 extending upwardly through the base 10 into threadedholes in the head 14. There are thus formed a series of cylindrical airchambers within the apparatus having a bottom section formed by thecircular openings 12 in the base 10 and a top section formed by thecircular openings 16 in the head 14. The diaphragm 18 serves to separatethe two sections with an air-tight seal.

Vertical passageways 22 are provided in the head 14 which communicatethe upper portion 16 of each air chamber with the uppermost face 23 ofthe head 14. The vertical passage 22 terminates at its uppermost end ina longitudinal slot 24. There is a longitudinal slot 24 for each airchamber to provide a series of longitudinal slots 24 along the face 23of the head 14. A thin wall 26 separates each pair of longitudinal slots24.

By this arrangement of longitudinal slots 24 a longitudinal voiddetecting area may be formed of any desired length, it being onlynecessary to multiply the number of air chambers and associatedlongitudinal slots 24 to increase the longitudinal detection area. Inoperation, the apparatus is placed transversely to the moving web ofpaper and hence substantially the entire width of the web passes overthe longitudinal detection area.

As the air chambers and associated elements are identical one to anotheronly one such air chamber will be herein desccribed.

A first electrical contact member is positioned in the air chamber bymounting a brass washer 28 on either side of the diaphragm 18, theradius of each washer 28 being slightly less than that of the circularopenings 12 and 16 which form the air chamber. A brass screw 30 ismounted through the center of the washers 28 and through the diaphragm18 and extends slidably through the base 10. A coiled spring 32 ispositioned around the screw 30 after it passes through the base and iscompressed against the base 10 by an adjustment nut 34. An upwardlyextending cut indicated generally at 36 may be provided in the bottom ofthe base 10 coaxial with the screw 30 to assist the seating of thespring 32 against the base 10. A locking nut 38 is positioned on thescrew 39 below the adjustment nut 34 to secure the adjustment nut 34when it is in proper operation position.

In order to provide means for drawing a vacuum through the upper airchamber and vertical passage 22 a narrow horizontal passage 40 isprovided in the head 14 communicating the upper air chamber 16 with alongitudinal passage 42 formed in the head 14 which is closed at one endand open at the other end to which a suitable vacuum line 66 may beattached. The passage 40 is sufficiently small to prevent the vacuum inline 66 from maintaining the vacuum in chamber 16 when a void occurs inthe web 62. Positioned through the side wall of the head 14, and inalignment with a flared opening 44 into the longitudinal passage 42formed at the end of the horizontal passage 40, is a screw 46 having aconical tip 48. The screw 46 thus provides valve means whereby thepassage of air through the horizontal passage 40 may be controlled andindividual detectors deactivated by advancing the screw 46 until the tip48 is seated in the opening 44.

A second contact member is positioned in the lower air chamber andcomprises a brass screw 50 positioned upwardly through the bottom of thebase 10 which is provided with a threaded opening to receive it. Thescrew contact 50 extends upwardly to a position slightly below thenormal operating position of the brass washer 28 which is positionedbelow the diaphragm 18. A locking nut 52 is provided for holding thecontact screw 50 in a predetermined position.

The head 14 is constructed with a slightly curved top face 23 which isdivided into three longitudinal segments by a pair of downwardly andoutwardly extending longitudinal cuts 54, 56 one out being positioned ashort distance either side of the series of longitudinal slots 24.Beveled side faces 58 are also provided on the head 14 through which aplurality of openings 60 are formed into the longitudinal cuts 54, 56.

The operation of my invention is as follows:

The apparatus is positioned transversely to a moving web of paper 62 asshown in FIG. 3. A pair of rollers 64 may be employed to guide the paperover the head 14. The vacuum line 66 is attached to the open end of thelongitudinal passage 42, and a vacuum, in practice, one suificient tosustain three inches of water, is drawn in the longitudinal passage 42.The screws 46, which serve as valve means are backed off so that thevacuum may draw through the horizontal passage 40, upper air chamber 16and vertical passage 22 of each detector assembly. The Web of paper 62is caused to move over the head 14 and consequently over the series oflongitudinal slots 24. The paper 62 is drawn down onto the longitudinalslots 24 causing the vacuum in the air chamber above the diaphragm 18 tolift the diaphragm 18, associated contact washers 23 and the brass screw30 as shown in FIG. 4. The contact screw 50 is positioned so that itwill not touch the washers 28 when the diaphragm is in raised position.

The brass screw 30 to which the washers 28 are fastened is connected bya lead wire 68 attached at its lower end to appropriate means forregistering an off-on electrical condition. A lead wire 70 connected tothe contact screw 56 is likewise connected to the registering means.

It will be apparent to one skilled in the art that the registering meansabove referred to may take the simple form of a source of electricalcurrent and an alarm hell or lamp wired in series with the leads 68, 70,or the leads 68, 7 0 may be connected to a sorter or other devicewhereby the defective paper is separated from the satisfactory paper.

When a void passes over one of the longitudinal slots 24, as shown inFIG. 5, outside air passes through the hole in the paper 62 and releasesthe vacuum in the air chambers above the diaphragm 18. This in turncauses the diaphragm 18, washers 28 and screw 30 to descend from theirraised operation position. The washer 23 below the diaphragm 18 makeselectrical contact with the screw contact 50 and consequently the alarmhell or other registering device is actuated. By suitable adjustment ofthe contact screw 50, and of the tension in the compressed coiled spring32 the apparatus may be caused to register any void passing over thelongitudinal slots 24.

The apparatus will also detect creases and wrinkles in the paper web.This is accomplished by the operation of the longitudinal cuts 54, 56.Assuming that the paper is moving from right to left over the head 14 asshown in FIGS. 4 and 5, it will be noted that a crease in the paperwould allow air to flow through the openings 60 and cut 54 over thenarrow longitudinal segment 72 of the top face 23 and down into the airchamber thereby actuating the apparatus. In this regard it should benoted that the longitudinal segment 72 should be as narrow as possiblein order to permit creases which are practically parallel to theapparatus to nonetheless actuate it.

The longitudinal cut 56 is provided to apply atmospheric pressure at theunder surface of the paper web after it has come over the longitudinaldetection slots 24 so that the paper will not bind as it is coming offthe head 14.

It will also be noted that the longitudinal cut 54 located prior to thedetection area serves a further important function of generallyequalizing the air pressure above and below the moving web. As the webis moving at high speed small amounts of air trapped between theengagement head 14 and the web due to vibration and oscillation of theweb as it approaches the apparatus may be dis charged through thelongitudinal cut 54 causing the web to pass smoothly over the detectionarea and simultaneously eliminating a possible source of false voidindications.

An alternative embodiment of my invention is shown in FIGS. 6 and 7 inwhich instead of drawing a vacuum through the apparatus, a slightpressure is applied. The only structural changes which are required arethat the compression spring 32 is mounted to urge the washers 28 andscrew 30 upwardly rather than downwardly, and the contact screw 50 ispositioned above the diaphragm 18 passing horizontally through the sideof the head 14. A conical tip 74 may be formed at the interior end ofthe contact screw 50 in order to permit close adjustment of the spacingbetween the contact screw 50 and the upper washer 28. It will be notedthat since the air is fed into the apparatus under pressure the normaloperating position of the diaphragm 18 is depressed, as shown in FIG. 6.When a hole or crease passes over the longitudinal detection slot 24 thepressure is released and the diaphragm is pushed upwardly by the spring32 so that the washer 28 contacts the contact screw 50 causing theapparatus to register a defect in the paper.

One advantage to the alternative embodiment using air under pressurerather than a vacuum is that any paper dust, etc., tending to accumulatein the apparatus is blown clear by the air flow.

It will also be obvious to one skilled in the art that the severaldetection areas are entirely independent in operation so that if it isdesired, they may be wired to separate registering means whereby thelocation of a void may be pin-pointed on the transverse dimension of theweb. It will also be noted that by providing separate valve screws 46for each air chamber the apparatus may be adjusted to operate with websof less width than the entire width of the apparatus.

It will be apparent from the above description that the pressure sensingchambers are in very close proximity to the paper surface, and thechambers themselves and all auxiliary chambers and air passagesconnecting thereto have been reduced to minimal volumes in order torender the device sufficiently sensitive to detect extremely small voidssuch as pinholes, passing at high speed.

It is my intention to claim all changes and modifications of thepreferred embodiment of my invention herein chosen for purposes ofdisclosure which do not constitute departures from the spirit and scopeof the invention.

What I claim as new and desire to secure by Letters Patent of the UnitedStates is:

1. In a void detector for a moving web, said detector having a detectorhead having an arcuate engagement face, first walls in said detectorhead defining passages from surface points on said face to at least onesensing chamber located said detector, said sensing chamber having adiaphragm member positioned in one wall thereof and having electricalcontact making elements associated therewith to indicate deflection ofsaid diaphragm from a first position, means for maintaining saiddiaphragm in a said first position including means for creating adifferential air pressure across said diaphragm and in said sensingchamber when said Web is continuous across said engagement face; meansfor introducing a supply of air at atmospheric pressure to theundersurface of said web in close proximity to said first walls in saiddetector head comprising second walls in said detector head defining atleast one passage from first surface points adjacent said first walls tosecond surface points open to the atmosphere, said first surface pointsbeing spaced a slight distance from said first walls whereby atmosphericpressure may be supplied to the undersurface of a moving web as said webpasses over said detector head to permit minor discrepancies in thestructure of said web to release said pressure differential in saidsensing chamber thereby actuating said electrical contact makingelements.

2. Structure for supplying air at atmospheric pressure to theundersurface of a web in a void detector as defined in claim 1 furthercharacterized by said means for supplying air at atmospheric pressurelocated closely adjacent said first walls and parallel thereto spaced ateach side thereof transversely to the direction of travel of said Web.

3. A void detector having an engagement head provided with an arcuateengagement face, a transversely elongated detector area in said facehaving a long narrow groove therein, a plurality of thin partitionsacross said groove to subdivide said groove into a plurality of adjacentsegments, first walls defining a large bore passage from each of saidsegments to an individual internal sensing chamber in said head for eachof said segments, each said internal sensing chamber having a flexiblediaphragm in one wall thereof, electrical contact means actuated bymotion of said flexible diaphragm, means for communicating air atnon-atmospheric pressure to said sensing chamber including second wallsin said detector head defining an air passage in communication with anexternal source for creating a differential air pressure across saidflexible diaphragm when a web completely covers said groove and thirdwalls defining a narrow bore metering passage between said sensingchamber and said air passage, and means for introducing a supply of airat atmospheric pressure to the undersurface of said web in closeproximity to said first walls in said detector head, said introducingmeans comprising fourth Walls in said detector head defining at leastone passage from first surface points adjacent said first walls tosecond surface points open to the atmosphere, said first surface pointsbeing spaced a slight distance from said first walls, wherebyatmospheric pressure may be supplied to the undersurface of a moving webas said web passes over said detector head to permit minor discrepanciesin the structure of said Web to release said pressure differential insaid sensing chamber thereby actuating said electrical contact means.

References Cited in the file of this patent UNITED STATES PATENTS1,588,831 Yokoyiama June 15, 1926 1,604,138 Vidaver Oct. 26, 19261,960,281 Schweizer May 29, 1934 2,244,864 Witham June .10, 19412,390,252 Hayward Dec. 4, 1945 2,794,444 Markey June 4, 1957 2,884,495Frankel Apr. 28, 1959 2,900,468 Joy Aug. 18, 1959

1. IN A VOID DETECTOR FOR A MOVING WEB, SAID DETECTOR HAVING A DETECTORHEAD HAVING AN ARCUATE ENGAGEMENT FACE, FIRST WALLS IN SAID DETECTORHEAD DEFINING PASSAGES FROM SURFACE POINTS ON SAID FACE TO AT LEAST ONESENSING CHAMBER LOCATED WITHIN SAID DETECTOR, SAID SENSING CHAMBERHAVING A DIAPHRAGM MEMBER POSITIONED IN ONE WALL THEREOF AND HAVINGELECTRICAL CONTACT MAKING ELEMENTS ASSOCIATED THEREWITH TO INDICATEDEFLECTION OF SAID DIAPHRAGM FROM A FIRST POSITION, MEANS FORMAINTAINING SAID DIAPHRAGM IN A SAID FIRST POSITION INCLUDING MEANS FORCREATING A DIFFERENTIAL AIR PRESSURE ACROSS SAID DIAPHRAGM AND IN SAIDSENSING CHAMBER WHEN SAID WEB IS CONTINUOUS ACROSS SAID ENGAGEMENT FACE;MEANS FOR INTRODUCING A SUPPLY OF AIR AT ATMOSPHERIC PRESSURE TO THEUNDERSURFACE OF SAID WEB IN CLOSE PROXIMITY TO SAID FIRST WALLS IN SAIDDETECTOR HEAD COMPRISING SECOND WALLS IN SAID DETECTOR HEAD DEFINING ATLEAST ONE PASSAGE FROM FIRST SURFACE POINTS ADJACENT SAID FIRST WALLS TOSECOND SURFACE POINTS OPEN TO THE ATMOSPHERE, SAID FIRST SURFACE POINTSBEING SPACED A SLIGHT DISTANCE FROM SAID FIRST WALLS WHEREBY ATMOSPHERICPRESSURE MAY BE SUPPLIED TO THE UNDERSURFACE OF A MOVING WEB AS SAID WEBPASSES OVER SAID DETECTOR HEAD TO PERMIT MINOR DISCREPANCIES IN THESTRUCTURE OF SAID WEB TO RELEASE SAID PRESSURE DIFFERENTIAL IN SAIDSENSING CHAMBER THEREBY ACUTATING SAID ELECTRICAL CONTACT MAKINGELEMENTS.